Adaptive beam forming as practiced in wireless communication is a communication technique using multiple antennas to either transmit an electromagnetic signal (hereinafter, simply signal) to, or receive a signal from a remote wireless station. Adaptive beam forming can be used to extend the range of the system. For example, the range may be extended by focusing energy in the direction of distant subscriber stations. Moreover, adaptive beam forming can mitigate the effects of interferers, by placing interfering subscriber stations within nulls in the beam pattern. Additionally, adaptive beam forming may increase the capacity of the system, such as through the user Spatial Division Multiple Access (SDMA). Since it can be practiced from either the transmit or the receive direction, it is most often (but not necessarily) practiced at the base station of a wireless carrier service provider.
A key to adaptive beam forming is the calculation of the weights that are applied to the incoming signals. There are a variety of techniques that vary in terms of the frequency with which weights are calculated, the granularity over which the weights are calculated (e.g., one weight for all subcarriers of the subchannel or individual weights for individual subcarriers), and the domain in which the processing is performed (e.g., analog vs. digital, and time domain vs. frequency domain). In Orthogonal Frequency Domain Multiple Access (OFDMA) systems, beam forming is often performed on each subchannel or group of subchannels allocated to a subscriber station. Further, the weights are preferably calculated adaptively, taking into consideration various factors including the channel conditions and/or the locations of the subscriber stations.
Typically, as more antennas are employed, the system exhibits more degrees of freedom, thereby allowing a system to form more beams and nulls. Thus, the more flexible system may be configured to support more remote stations and/or more SDMA users. However, the complexity of the weight calculation increases as more antennas are employed and/or more SDMA users are supported. Also space and cost considerations at the deployment site often constrain the number of antennas that can be deployed in a cost effective manner. Thus, there is a wide range of base station needs, depending on the area and/or the number of users supported, and/or the number of antennas employed. This wide range of needs present a challenge to the system integrator and the component suppliers.